Contrary to popular belief, pre-exercise food does NOT simply sit in the stomach and hinder athletic performance. Rather, it enhances stamina and endurance. The following study confirms this point:
On two occasions, athletes exercised moderately hard until they were exhausted. In one trial, they ate a 400-calorie breakfast three hours before exercising. In the second trial, they simply had a dinner the night before. When they exercised "on empty," they biked for only 109 minutes, as compared to 136 minutes with the breakfast. That's almost half an hour longer! Exercising without fuel left them lagging. (Med Sci Sports Exerc 31(3):464, 1999)
Even if you eat five minutes before exercise, you’ll digest the snack and burn it during exercise, assuming you will be exercising at a pace you can maintain for more than 30 minutes. This means, you can enjoy a granola bar and banana on the way to the gym to fuel your workout. Research suggests this pre-exercise snack can help you perform 10% harder in the last 10 minutes of a one-hour workout. Go for it!
Your goal is to target 0.5 grams carbohydrate per pound of body weight within the hour before you exercise. This means, if you weigh 150 pounds, you should target about 300 calories. This is far more than most athletes consume. Obviously, the amount will depend on your stomach's tolerance to pre-exercise fuel. If you have a finicky stomach, liquids or semi-solids (Boost, yogurt, applesauce, pudding) might empty from the stomach quicker than oatmeal, bagel, banana, animal crackers or graham crackers. The trick is to teach your intestinal track to tolerate the pre-exercise food so you can enjoy higher energy but avoid undesired pit stops.